| String Area Properties |
 | | Stringing machine | Reducing the tension in the strings can produce a more flexible string area or 'lower stringbed stiffness'. For a groundstroke, a 25% decrease in tension corresponds to a 2% increase in speed, a serve profits from just a 1% increase.
The stiffness of the stringbed is also affected by the arrangement of the strings. If the space between strings is increased the face becomes more flexible. Similarly, increasing the length of the strings, by enlarging the head for example, lowers the stiffness of the stringbed.
Several reasons have been proposed to explain that reducing the stiffness of the string area is detrimental to control:
1. The hitting surface distorts more during impact, increasing the range of angles at which the ball may fly off.
2. The ball deforms less, so the size of the contact area, which helps to direct the ball, is diminished.
3. The dwell time is extended, so the racket can rotate further during impact, which reduces the control the player has over the racket.
A benefit of the increased dwell time is that a smaller force is spread over a longer period, resulting in reduced shock on impact.
String gauge
The diameter of a string is more commonly referred to as its gauge. The more popular gauges lie between 1 and 1.5 mm, or 15 to 18 on the American scale: See table 1.
A thinner gauge makes the string more flexible, but also reduces its durability as less time is needed to saw through the string. Minute movements between the strings tend to abrade them until they eventually snap at the point of intersection. Although thinner strings are believed to impart more spin on the ball, there is little empirical evidence to support this theory. There is also no appreciable difference in spin produced by rough or smooth, low- or high-tension strings.
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| European gauge | US gauge | Inches | Milimeters | | 12 | 13 | 0.065 - 0.071 | 1.65 - 1.80 | | 11 | 14 | 0.059 - 0.065 | 1.50 - 1.65 | | 9.5 | 15 | 0.056 - 0.059 | 1.41 - 1.49 | | 9 | 15L | 0.052 - 0.056 | 1.33 - 1.41 | | 8.5 | 16 | 0.050 - 0.053 | 1.26 - 1.34 | | 8 | 16L | 0.048 - 0.051 | 1.22 - 1.30 | | 7.5 | 17 | 0.046 - 0.049 | 1.16 - 1.24 | | 7 | 18 | 0.042 - 0.046 | 1.06 - 1.16 | | 4 | 19 | 0.035 - 0.042 | 0.90 - 1.06 | | 3.5 | 20 | 0.031 - 0.035 | 0.80 - 0.90 | | 3 | 21 | 0.028 - 0.031 | 0.70 - 0.80 | | 2.5 | 22 | 0.024 - 0.028 | 0.60 - 0.70 |
 | | Spaghetti stringing | Stringing systems
According to the Rules of Tennis, "the hitting surface of the racket shall be flat and consist of a pattern of crossed strings connected to a frame and alternately interlaced or bonded where they cross" (rule 4a). This tends to limit the movement between strings and, thus, the spin imparted to the ball. This rule was introduced in 1978 in response to a stringing system patented the previous year (US Patent 4273331, 8 December 1977) which could generate almost twice as much spin as a conventionally-strung racket, dubbed 'spaghetti' stringing.
Spaghetti stringing is illegal because the main and cross strings are not interlaced (or bonded). Instead, the strings lie on parallel planes and are able to move with the aid of tubular sleeves, which act as bearings, see below.
The freedom of movement allows the strings to deflect within the plane of the hitting surface and so rotate the ball as they recoil. The result is that players can produce extreme spin with minimal effort.
Click here to see pictures of different stringing systems.
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